CVE-2023-6879: Aomedia Buffer Overflow Vulnerability

CVE-2023-6879 Overview

CVE-2023-6879 is a heap overflow vulnerability affecting the AOMedia AV1 video codec library. The vulnerability occurs in the av1_loop_restoration_dealloc() function when increasing the resolution of video frames during a multi-threaded encoding operation. This memory corruption flaw can be exploited remotely without requiring user interaction or authentication, potentially allowing attackers to execute arbitrary code or cause system crashes.

Critical Impact

This heap overflow vulnerability in the widely-used AV1 codec library can be exploited remotely to achieve arbitrary code execution, potentially compromising systems that process malicious video content.

Affected Products

• AOMedia AOM (libaom) prior to version 3.7.1
• Fedora 38 (with affected aom packages)
• Fedora 39 (with affected aom packages)

Discovery Timeline

• December 27, 2023 - CVE-2023-6879 published to NVD
• February 13, 2025 - Last updated in NVD database

Technical Details for CVE-2023-6879

Vulnerability Analysis

This vulnerability is classified under CWE-787 (Out-of-bounds Write) and CWE-20 (Improper Input Validation). The flaw exists within the loop restoration deallocation routine of the AV1 encoder. When processing video streams that dynamically change resolution during multi-threaded encoding operations, the codec fails to properly manage heap memory allocations.

The AOMedia AV1 codec is extensively used across modern web browsers, video streaming platforms, and multimedia applications. The network attack vector means this vulnerability can be triggered remotely by processing specially crafted video content, requiring no privileges or user interaction. This makes it particularly dangerous in scenarios where systems automatically process user-supplied video files or streams.

Root Cause

The root cause lies in improper memory management within the av1_loop_restoration_dealloc() function. When video frame resolution is increased during an active multi-threaded encoding session, the function does not correctly validate or reallocate the necessary heap buffers. This leads to a mismatch between the expected buffer size and the actual allocated memory, resulting in heap memory being overwritten beyond its intended boundaries.

Attack Vector

The vulnerability can be exploited through network-based delivery of malicious video content. An attacker could craft a video file that triggers resolution changes during encoding, targeting systems that process AV1 video content. Potential attack vectors include:

• Uploading malicious video files to platforms that transcode content using the vulnerable library
• Streaming crafted video content to applications using the affected AV1 encoder
• Embedding malicious video content in web pages targeting browsers with vulnerable codec implementations

The heap overflow occurs during the deallocation and reallocation process when handling resolution changes, allowing an attacker to potentially corrupt adjacent heap metadata or overwrite critical data structures for code execution.

Detection Methods for CVE-2023-6879

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using the AV1 codec library
• Abnormal memory allocation patterns or heap corruption indicators in multimedia processing services
• Error logs referencing av1_loop_restoration_dealloc() or related AV1 encoding functions
• Unusual process behavior following video content processing operations

Detection Strategies

• Monitor for heap corruption exceptions in applications utilizing libaom or AV1 encoding functionality
• Implement application-level monitoring for abnormal memory usage during video encoding operations
• Deploy endpoint detection and response (EDR) solutions capable of identifying memory corruption exploitation attempts
• Review system and application logs for AV1-related crashes or errors

Monitoring Recommendations

• Configure monitoring for video processing applications to detect unusual resource consumption patterns
• Enable heap protection mechanisms and monitor for heap integrity violations
• Implement file integrity monitoring on AV1 codec library files to detect unauthorized modifications
• Track version information of installed libaom packages to ensure patched versions are deployed

How to Mitigate CVE-2023-6879

Immediate Actions Required

• Update AOMedia libaom library to version 3.7.1 or later immediately
• Apply Fedora security updates for affected aom packages on Fedora 38 and 39 systems
• Audit systems for applications that bundle or statically link the vulnerable libaom library
• Consider temporarily disabling AV1 encoding functionality in critical systems until patches are applied

Patch Information

AOMedia has released version 3.7.1 which addresses this vulnerability. The fix can be obtained from the AOMedia Release Notes v3.7.1. Additional technical details about the vulnerability can be found in the Chromium Bug Report #3491.

Fedora has issued package announcements with updated packages for Fedora 38 and Fedora 39. Users should apply these updates through the standard package management system.

Workarounds

• Restrict processing of untrusted video content on systems using vulnerable libaom versions
• Disable multi-threaded encoding if possible until the patch can be applied
• Implement network segmentation to isolate video processing systems from untrusted sources
• Apply strict input validation on video files before processing with the AV1 encoder

# Update libaom on Fedora systems
sudo dnf update libaom

# Verify installed version is 3.7.1 or later
rpm -q libaom